HYP2018: 13th International Conference on Hypernuclear and Strange Particle Physics

Studying Λ interactions in nuclear matter with the 208Pb(e,e'K+)208Tl reaction

Not scheduled

15m

2nd Floor

Abstract Submission

Speaker

Dr Franco Garibaldi (INFN)

Description

The recent observation of 2-solar-mass neutron-stars rules out most of the current models for the hyperonic matter equation of  state which favour the appearance of hyperons in the neutron  star interior but predict maximum masses (Mmax) incompatible with present data. This problem, known as the hyperon-puzzle, is presently a subject of very active research. A solution to it necessarily requires a better knowledge of the nuclear interaction involving hyperons. Due to the short lifetime of hyperons, the information provided by the available scattering data  in the hyperon-nucleon (YN) sector is scarce, and does not allow the determination of the YN interaction using the same scheme successfully employed in the nucleon-nucleon (NN) sector. In the absence of scattering data, alternative information on the YN interaction can be obtained from hypernuclear physics. Hypernuclear spectroscopy appears to be the only practical way to study baryonic forces, and may play a significant role towards the solution of the so-called hyperon puzzle. Precise hypernuclear spectroscopy on medium to heavy hypernuclei with electron beams, which is only possible with the CEBAF electron beam, is critically important to obtain new information needed to constrain theoretical models of neutron star matter. The measured charge density distribution of 208Pb [1] clearly shows that the region of nearly constant density accounts for a very large fraction (~70 %) of the nuclear volume, thus suggesting that its properties largely reflect those of uniform nuclear matter in the neutron star interior. The validity of this conjecture has been long established by a comparison between the results of theoretical calculations and the data extracted from the 208Pb(e,e´p)207Tl cross sections measured at NIKHEF in the 1980s [2,3]. The energy dependence of the spectroscopic factors, obtained from the analysis of the measured missing energy spectra, turns out to be in remarkably good agreement with the results reported in the pioneering work of Ref. [4]. Microscopic calculations of the Λ spectral function in a variety of nuclei, ranging from 5He to 208Pb, have been recently carried out [5]. The results of this analysis—based on a realistic hyperon-nucleon potential model constrained by the available scattering data—suggest that hyperon dynamics in 208Pb may be somewhat different compared to lighter nuclei, as signaled by a larger quenching of the spectroscopic factors. In view of its important astrophysical implications, the extension of the (e,e´K+) experimental program of Jefferson Lab to a heavy nuclear target with a large neutron excess, such as 208Pb, is of primary importance. The study of the 208Pb(e,e'K+)208Ti reaction will provide information on the properties of a bound hyperon in an environment little affected by surface and shell effects. It is complementary to the measurements that will be performed using 40Ca and 48Ca targets, whose main purpose is the analysis of the isospin dependence of hyperon dynamics. A proposal for studying the 208Pb(e,e'K+)208Ti reaction at Jefferson Lab Hall A is going to be submitted to the next Jefferson Lab PAC. 1. B. Frois and C. N. Papanicolas, Ann. Rev. Nucl. Part. Sci. 37, 133 (1987). 2. E. N. Quint et al., Phys. Rev. Lett. 56, 186 (1986); E. N. Quint et al., Phys. Rev. Lett. 58, 1727 (1987). 3. M. van Batenburg, PhD Thesis, University of Utrecht, 1996. 4. O. Benhar, A. Fabrocini, and S. Fantoni, Phys. Rev. C 41, R24 (1990). 5. I. Vidaña, Nucl. Phys. 958, 468 (2017). 6. J.C. David, C. Fayard, G.-H. Lamot, B. Saghai, Phys. Rev. C 53, 2613 (1996); T. Mizutani, C. Fayard, G.-H. Lamot, B. Saghai, Phys. Rev. C 58, 75 (1998). 7. “Spectroscopy of Λ hypernuclei,” Review paper, O. Hashimoto and H. Tamura, Progress inParticle and Nuclear Physics 57 (2006).

Summary

The recent observation of 2-solar-mass neutron-stars rules out most of the current models for the hyperonic matter equation of  state which favour the appearance of hyperons in the neutron  star interior but predict maximum masses (Mmax) incompatible with present data.
This problem, known as the hyperon-puzzle, is presently a subject of very active research. A solution to it necessarily requires a better knowledge of the nuclear interaction involving hyperons. Due to the short lifetime of hyperons, the information provided by the available scattering data  in the hyperon-nucleon (YN) sector is scarce, and does not allow the determination of the YN interaction using the same scheme successfully employed in the nucleon-nucleon (NN) sector.
In the absence of scattering data, alternative information on the YN interaction can be obtained from hypernuclear physics. Hypernuclear spectroscopy appears to be the only practical way to study baryonic forces, and may play a significant role towards the solution of the so-called hyperon puzzle.
Precise hypernuclear spectroscopy on medium to heavy hypernuclei with electron beams, which is only possible with the CEBAF electron beam, is critically important to obtain new information needed to constrain theoretical models of neutron star matter.
The measured charge density distribution of 208Pb [1] clearly shows that the region of nearly constant density accounts for a very large fraction (~70 %) of the nuclear volume, thus suggesting that its properties largely reflect those of uniform nuclear matter in the neutron star interior. The validity of this conjecture has been long established by a comparison between the results of theoretical calculations and the data extracted from the 208Pb(e,e´p)207Tl cross sections measured at NIKHEF in the 1980s [2,3].
The energy dependence of the spectroscopic factors, obtained from the analysis of the measured missing energy spectra, turns out to be in remarkably good agreement with the results reported in the pioneering work of Ref. [4].
Microscopic calculations of the Λ spectral function in a variety of nuclei, ranging from 5He to 208Pb, have been recently carried out [5]. The results of this analysis—based on a realistic hyperon-nucleon potential model constrained by the available scattering data—suggest that hyperon dynamics in 208Pb may be somewhat different compared to lighter nuclei, as signaled by a larger quenching of the spectroscopic factors.
In view of its important astrophysical implications, the extension of the (e,e´K+) experimental program of Jefferson Lab to a heavy nuclear target with a large neutron excess, such as 208Pb, is of primary importance. The study of the 208Pb(e,e'K+)208Ti reaction will provide information on the properties of a bound hyperon in an environment little affected by surface and shell effects. It is complementary to the measurements that will be performed using 40Ca and 48Ca targets, whose main purpose is the analysis of the isospin dependence of hyperon dynamics.
A proposal for studying the 208Pb(e,e'K+)208Ti reaction at Jefferson Lab Hall A is going to be submitted to the next Jefferson Lab PAC.

1. B. Frois and C. N. Papanicolas, Ann. Rev. Nucl. Part. Sci. 37, 133 (1987).
2. E. N. Quint et al., Phys. Rev. Lett. 56, 186 (1986); E. N. Quint et al., Phys. Rev. Lett. 58, 1727 (1987).
3. M. van Batenburg, PhD Thesis, University of Utrecht, 1996.
4. O. Benhar, A. Fabrocini, and S. Fantoni, Phys. Rev. C 41, R24 (1990).
5. I. Vidaña, Nucl. Phys. 958, 468 (2017).
6. J.C. David, C. Fayard, G.-H. Lamot, B. Saghai, Phys. Rev. C 53, 2613 (1996);
   T. Mizutani, C. Fayard, G.-H. Lamot, B. Saghai, Phys. Rev. C 58, 75 (1998).
   1. “Spectroscopy of Λ hypernuclei,” Review paper, O. Hashimoto and H. Tamura,
      Progress inParticle and Nuclear Physics 57 (2006).